1. Field of the Invention
The present invention relates to an Integrated Services Digital Network (ISDN) switching system which incorporates therein testing facilities for ISDN signals.
ISDN has been internationally standardized for integrally supporting worldwide communications for a variety of media services such as speech signals, computer data signals, picture signals and so on.
Along with the progress of ISDN, it is also required to improve reliability in communications, and therefor, testing facilities for B-channel signals and D-channel signals must be incorporated in the ISDN switching system.
2. Description of the Related Art
As will be explained in detail hereinafter, conventional testing facilities involve some problems.
In short, regarding the D-channel test, it is very difficult to achieve a monitoring test and a bit error measurement for the D-channel signals per se. This is because, the D-channel signals are terminated at a Link Access Procedure on the D-channel (LAPD) termination unit in each Digital subscriber Line Circuit Controller (DLCC). Therefore, if a test for the D-channel signal per se is required, the test facilities must prepare a great number of testing cables to be connected to the input/output terminals of each LAPD.
Regarding the B-channel test, known as a Bridge Cut-Off (BCO) test, the following problems have arisen.
i) Many sets of test use ISDN terminal equipment are needed, since many sets of Digital subscriber Line & Trunk test Equipment (DLTE) are used for each ISDN exchange which is coupled with the corresponding test use ISDN terminal equipment. Further more sets of the test use ISDN terminal equipment must be employed if the ISDN switching system is set up with a plurality of remote local switches.
ii) If the BCO test must be carried out for a subscriber accommodated in the remote local switch, usually unmanned switch, an operator must go to the remote local switch to operate the test use ISDN terminal equipment.
iii) If the BCO test is to be carried out under control of a Central Maintenance Operation Center (CMOC), test use cables must be provided for the connection between the CMOC and each local switch. This prevents an easy expansion of the BCO test.